/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.resolver;

import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.Future;
import io.netty.util.internal.UnstableApi;

import java.net.InetAddress;
import java.net.InetSocketAddress;

/**
 * A skeletal {@link NameResolver} implementation that resolves {@link InetAddress}.
 */
@UnstableApi
public abstract class InetNameResolver extends SimpleNameResolver<InetAddress> {

  private volatile AddressResolver<InetSocketAddress> addressResolver;

  /**
   * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link
   * Future} returned by {@link #resolve(String)}
   */
  protected InetNameResolver(EventExecutor executor) {
    super(executor);
  }

  /**
   * Return a {@link AddressResolver} that will use this name resolver underneath. It's cached
   * internally, so the same instance is always returned.
   */
  public AddressResolver<InetSocketAddress> asAddressResolver() {
    AddressResolver<InetSocketAddress> result = addressResolver;
    if (result == null) {
      synchronized (this) {
        result = addressResolver;
        if (result == null) {
          addressResolver = result = new InetSocketAddressResolver(executor(), this);
        }
      }
    }
    return result;
  }
}
